Chondrocyte cell death is a central component of many degenerative cartilage diseases, such as osteoarthritis and temporomandibular joint disorders, and thus has a substantial public health impact. By investigating a zebrafish mutant with a malformed head skeleton, this project has identified impaired exocytosis as a potentially novel mechanism of chondrocyte apoptosis and cartilage degradation within the neurocranium and pharyngeal arches, leading to clefting of the ethmoid plate. In this mutant, the onset of cartilage degradation develops after initial cartilage deposition. Thus, this mutation disrupts the maintenance but not the formation of cartilage and is similar in progression to some forms of osteoarthritis and other degenerative cartilage diseases. Through the use of forward genetics and positional cloning, this approach has also identified a novel gene necessary for craniofacial development and chondrocyte cell survival. The goals of this project are a) to identify whether this gene is required cell-autonomously or non cell-autonomously for chondrocyte cell survival and b) to define the mechanism by which loss of this gene function leads to chondrocyte cell death. Approaches for testing the cell autonomous function of this gene will include the use of zebrafish genetics and cell transplantation experiments. Mechanistic studies will also use in vivo analyses and imaging approaches. By exploring the function of this novel gene during craniofacial morphogenesis, this project identifies a new mechanism leading to chondrocyte cell death and cartilage degradation. These key discoveries highlight the importance of further studies in animal models. Findings obtained during the course of the proposed study may have important translational impact with respect to the pathophysiology of degenerative cartilage diseases. Moreover, because the zebrafish mutant phenotype analyzed here leads to clefting of the neurocranium, the results of these studies may provide a link between congenital orofacial clefts and adult cartilage diseases.